Master Gardener: Night crawlers are a gardener’s friend

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If you see holes like this in the ground, with debris around the entrance and little piles of castings nearby, there’s a good chance they were created by earthworms, AKA night crawlers. These creatures help aerate the soil, and their castings serve as pre-digested nutrients for plants. Photo by Jack Kelly Clark, courtesy UC Statewide IPM Program

Q I’ve been noticing odd little holes in the soil around my yard. There are little piles of dirt alongside them. The holes are smaller in diameter than a pencil, and at least an inch or more deep. What causes this? We had a yellowjacket problem last year; this couldn’t be a yellowjacket ground nest, could it?

A Very small holes in the ground can be created by a number of creatures. Spiders, ants, worms and, yes, bees make small holes in which to live or nest. Many bees and wasps use abandoned rodent holes. Some bees create their own new holes.

Clues around the holes may help with identification. Wolf spiders living in their holes create no webs, but there might be a bit of silk around the opening. Funnel spiders have an obvious funnel-shaped web leading right into the hole. Some ants leave a cone of excavated dirt around the opening, while other ants do not. Many creatures such as the earthworm will have debris around the hole, leaving little piles of dirt called castings.

Another clue as to what the holes might be is the season of the year. You will see more holes created by earthworms in the wet season than in dry months.

Our native bees and bumblebees either find an existing hole or create one. The female brings pollen and nectar into the hole and lays an egg on top of this cache. She then seals off the chamber and repeats this process with the next egg. Native bees and bumblebees nest in the spring.

Yellowjackets typically build a more complex, chambered nest below ground. As with ants, the nest is busy with occupants coming and going all day. Yellowjackets typically nest in the fall.

Paper wasps build nests under eaves, etc., and do not nest in the ground.

The holes you describe seem to match the type created by the humble earthworm, or night crawlers, as they are sometimes called. Earthworms help aerate the soil, and their castings are wonderfully predigested nutrients for plants!

More information can be found at these links. They contain information on worms, wasps, spiders and solitary bees.

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